Meeting the Climate-Change Challenge John P. Holdren Teresa & John Heinz Professor of Environmental Policy and Professor of Earth and Planetary Sciences Harvard University Director, The Woods Hole Research Center Chair of the Board, AAAS The John H. Chafee Memorial Lecture National Council for Science and the Environment Washington DC • 17 January 2008 Main messages • “Global warming” is a misnomer; we should be calling it “global climatic disruption”. • The disruption & its impacts are now growing more rapidly than was expected just a few years ago. • The world is already experiencing “dangerous anthro- pogenic interference in the climate system”. The question now is whether we can avoid catastrophic interference. • Our options are mitigation, adaptation, & suffering. If we do less mitigation & adaptation, we’ll do more suffering. • In mitigation and adaptation, there is a lot of “low-hanging fruit”, but it’s not enough. We need a price on GHG emissions to motivate reaching higher in the tree, as well as R&D to bring more fruit into reach. • The United States must switch from laggard to leader – and sooner rather than later – if the world is to act in time. 1
What climate is & what climate change means Climate is the pattern of weather, meaning averages, extremes, timing, spatial distribution of… • hot & cold • cloudy & clear • humid & dry • drizzles & downpours • snowfall, snowpack, & snowmelt • zephyrs, blizzards, tornadoes, & typhoons Climate change means altered patterns. Global average temperature is just an index of the state of the global climate as expressed in these patterns. Small changes in the index � big changes in the patterns. What climate change puts at risk Climate governs (so climate change affects) • availability of water • productivity of farms, forests, & fisheries • prevalence of oppressive heat & humidity • formation & dispersion of air pollutants • geography of disease • damages from storms, floods, droughts, wildfires • property losses from sea-level rise • expenditures on engineered environments • distribution & abundance of species 2
The Earth is getting hotter. Green bars show 95% confidence intervals 2005 was the hottest year on record; the 14 hottest all occurred since 1990, 24 out of the 25 hottest since 1980. http://data.giss.nasa.gov/gistemp/graphs/ What’s happening reverses a long cooling trend “Proxy” temperature reconstructions + 125-yr thermometer record National Research Council, 2006 T leveled off ~1600, started to rise after 1700 & more sharply after 1800. 3
We know why: Human vs natural influences 1750-2005 (watts/m 2 ) Human emissions leading to increases in… atmospheric carbon dioxide + 1.7 methane, nitrous oxide, CFCs + 1.0 net ozone (troposphere ↑ , stratosphere ↓ ) + 0.3 absorptive particles (soot) + 0.3 reflective particles (sulfates, etc.) - 0.7 indirect (cloud forming) effect of particles - 0.7 Human land-use change increasing reflectivity - 0.2 Natural changes in sunlight reaching Earth + 0.1 The warming influence of anthropogenic GHG and absorbing particles is ~30x the warming influence of the estimated change in input from the Sun. IPCC AR4, WG1 SPM, 2007 The key greenhouse-gas increases were caused by human activities. Compared to natural changes over the past 10,000 years, the spike in concentrations of CO 2 & CH 4 in the past 250 years is extraordinary. We know humans are responsible for the CO 2 spike because fossil CO 2 lacks carbon-14, and the drop in atmospheric C-14 from the fossil-CO 2 additions is measurable. IPCC AR4, WG1 SPM, 2007 4
The smoking gun for human influence Top panel shows best estimates of human & natural forcings 1880-2005. Bottom panel shows that state-of-the-art climate model, fed these forcings, reproduces almost perfectly the last 125 years of observed temperatures. Source: Hansen et al., Science 308 , 1431, 2005. The current heating is not uniform geographically Average T for 2001-2005 compared to 1951-80, degrees C J. Hansen et al., PNAS 103 : 14288-293 ( 2006) 5
Circulation patterns are changing Weakening of the East Asia Monsoon is an example 2.8 45 Windy days with daily mean wind speed >5m/s (day) wind speed 2.7 windy days 40 2.6 Mean wind speed (m/s) 35 Y = -0.02161X + 45.275 2.5 (R 2 = 0.94, p < 0.001) 2.4 30 2.3 25 Y = -0.8022X + 1620.66 (R 2 = 0.95, p < 0.001) 2.2 20 2.1 Qi Ye, Tsinghua University, May 2006 2.0 15 1965 1970 1975 1980 1985 1990 1995 2000 2005 Year Chinese studies conclude that this phenomenon is indeed a result of greenhouse-gas-driven global climatic change. Evaporation & precipitation are increasing NCDC, 2000 Effect is not uniform; most places getting wetter, some getting drier. 6
Permafrost is thawing Average ground temperature near Fairbanks, Alaska, degrees C Permafrost thaws when T ≥ 0°C ACIA 2004 Arctic summer sea ice is disappearing September 2005 September 2007 US National Snow & Ice Data Center, 2007 7
Surface melting on Greenland is expanding 1992 2002 2005 In 1992 scientists measured this Ten years later, in 2002, the And in 2005, it accelerated amount of melting in Greenland as melting was much worse dramatically yet again indicated by red areas on the map Source: ACIA, 2004 and CIRES, 2005 Sea-level is rising mm ACIA, 2004 1993-2003 ≈ 30 mm = 3.0 mm/yr; compare 1910-1990 = 1.5±0.5 mm/yr. 8
These changes are already causing harm Major floods per decade, 1950-2000 There’s a consistent 50-year upward trend in every region except Oceania. Harm is already occurring (continued) Wildfires in the Western USA have increased 4-fold in the last 30 years. Western US area burned Source: Westerling et al. 2006 9
Harm is already occurring (continued) Total power released by tropical cyclones (green) has increased along with sea surface temperatures (blue). Source: Kerry Emanuel, MIT, http://wind.mit.edu/~emanuel/anthro2.htm. SST anomaly (deg C) with arbitrary vertical offset. PDI scaled by constant. Kerry Emanuel, MIT, 2006 Harm is already occurring (continued) Weakening East-Asia monsoon has meant less moisture flow South to North, producing increased flooding in South, drought in North S # S # B S Precipitation trend S S S S # S S # (mm/decade) S # # S # # # S S # S S # S # # # # # S # # # S # S S S # S S # S # # # S S # S # # S # S S S # S # # # S S # S S S S ## S S S # # # S S S # # # # S # S # # S S # S # # S S S S # # # <-60 S # S # # S S S # # # # # S # # S S # S # S # # # S # -60 S S S # # # # # # # S S # # # # # # -40 S S # # # # # S # # # # S # # # S # S # S # # S S S -20 S # S S S # S S # # S S S S S S S # S S S S S # S S S S S S S S S S # SS S 0 # S S # # # S S S S S S S S S S S # S # S S S 20 S S S S S S S S # S S # S S S S S S S S 40 S # # # # S S S # S S S # # # S S # S S S S # 60 # S S S # # S # # # # # # # # S # S S S >60 S S # # S Qi Ye, Tsinghua University, May 2006 10
Harm is already occurring (continued) The Amazon is drying & burning Drying results from combined effects of altered regional atmospheric circulation linked to global climate change and local influence of deforestation itself. Nepstad et al., Forest Ecology & Management 154, 2001 Harm is already occurring (concluded) WHO estimates climate change already causing ≥ 150,000 premature deaths/yr in 2000 11
Bigger disruption is coming: IPCC 2007 scenarios Last time T was 2ºC above 1900 level was 130,000 yr BP, with sea level 4-6 m higher than today. Last time T was 3ºC above 1900 level was ~30 million yr BP, with sea level 20-30 m EU target ∆ T ≤ 2ºC higher than today. Note: Shaded bands denote 1 standard deviation from mean in ensembles of model runs IPCC 2007 Where we’re headed: Heat waves Extreme heat waves in Europe, already 2X more frequent because of global warming, will be “normal” in mid-range scenario by 2050 Black lines are observed temps, smoothed & unsmoothed; red, blue, & green lines are Hadley Centre simulations w natural & anthropogenic forcing; yellow is natural only. Asterisk and inset show 2003 heat wave that killed 35,000. Stott et al., Nature 432 : 610-613 (2004) 12
Higher temperatures also mean more smog 0.30 Daily Maximum Ozone (ppm) 0.25 0.20 South Coast Air 0.15 Basin Ozone Levels 0.10 (1996-1999) 0.05 0.00 40 60 80 100 120 Mean Maximum Temperature ( o F) Our Changing Climate: Assessing the Risks to California (2006), www.climatechange.ca.gov. Source: Air Resources Board, 2000 Where we’re headed: Agriculture in the tropics Crop yields in tropics start dropping at local ∆ T ≥ 1-1.5°C Easterling and Apps, 2005 13
Where we’re headed: Temperate-zone agriculture Temperate-zone crop yields start dropping at local ∆ T ≥ 1-2°C Drops are more gradual than in tropics, but still significant. Easterling and Apps, 2005 Where we’re headed: droughts Drought projections for IPCC‘s A1B scenario Percentage change in average duration of longest dry period, 30-year average for 2071-2100 compared to that for 1961-1990. 14
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